Refrigerator Thermostat Replacement Device

When the refrigerator's thermostat is damaged and it is difficult to install a new one, the electronic thermostat introduced in this article can be used as an emergency substitute.

How it works

The circuit working principle of the device is shown in Figure 1. It uses a time-based integrated circuit NE555 as a cycle timing controller. When the power is turned on, since the ② and ⑥ pins of IC1 are low, IC1 is triggered and set, and its ③ pin becomes high. At this time, relay J is excited and attracted, its normally closed contact j1 is disconnected, and R5 does not work. At the same time, the normally open contact j2 is closed, and the refrigerator is powered on and starts to work and cool. At this time, since the ③ pin of IC1 is in a high-level state, the diode VD6 is turned on, and the current charges C1 through resistors R1 and R2. As time goes by, when the voltage across C1 rises to 2/3 of the power supply voltage, IC1 automatically resets, its ③ pin becomes low, and the corresponding relay J also loses power and releases, and the refrigerator stops working. After stopping working, since the ③ pin of IC1 is low, j1 connects R5 at this time. Due to the connection of R5, the threshold voltage of IC1 is not 1/3 of the power supply voltage, but 1/2 of the voltage of IC1 ⑤ pin. At this time, C1 is discharged through R3, R4 and the internal discharge tube of IC1. When the voltage on C1 drops to about 1V, IC1 flips back to the set position, that is, the ③ pin of IC1 turns to high level again. Therefore, due to the connection of R5, the smaller resistance values ​​of R3 and R4 can obtain a longer delay, and the difference in charging time between the first and subsequent times can also be reduced. According to the values ​​of the schematic diagram, R2 and R3 can be adjusted appropriately, so that the start and shutdown time of the refrigerator can be controlled to change within 5-15 minutes respectively. In order to extend the shutdown time of the refrigerator, the resistance value of R5 can also be appropriately reduced.

Component selection and production

The components list is shown in the table below.

When using, according to the changes in different seasons, the resistance values ​​of R2 and R3 should be adjusted appropriately to make the minimum and maximum temperatures of the refrigerator meet the required requirements. Generally, the difference between the maximum and minimum temperatures in the refrigerator should be controlled between 6-10℃, the start-stop ratio per hour should not exceed 8, and the shutdown time of each time should be adjusted to no less than 5 minutes.

After the circuit is debugged, it can be installed in the plastic case, and the socket CZ can also be installed separately